The present invention relates to a process for the preparation of tertiary alcohols by the hydration of tertiary olefins on an acidic ion exchanger in a reactive rectification using a structured multi-purpose packing.
From U.S. Pat. No. 2,813,908, it is already known to hydrate olefins on styrene-divinyl-benzene polymers containing sulfonic acid groups. This process is performed at temperatures of from 121 to 218° C. and pressures of up to 211 bar, but when isobutene is used, it results in an extensive formation of isobutene polymers.
Especially known from U.S. Pat. No. 3,257,469 is the preparation of tertiary amyl alcohol (TAA) on such acidic ion exchangers containing sulfonic acid groups by the reaction of isoamylene with a molar excess of water. This is effected, for example, at a pressure of 35 bar and a temperature of from 66 to 107° C. A proportion of TAA in the reaction product which is sufficient for industrial purposes is achieved by including solvents, of which isopropanol and acetone are particularly pointed out. Thus, this process necessarily comprises the separation of the included solvent from the reaction mixture.
U.S. Pat. No. 4,182,920 is a further development of the previously described process and is also preferably aiming at the preparation of TAA. A novel feature particularly pointed out is that the whole feed mixture forms a single homogeneous phase and part of the isoamylene is fed into a second of a total of at least two reactors. As the solvent, acetone is particularly pointed out, and according to the Examples, it is present in an amount of from 60 to 75% by weight of the whole feed. This process is also performed with excess molar amounts of hydration water.
DE-A-35 12 518 describes the catalytic hydration of lower olefins, which are propene and n-butene according to the Examples. As the reaction parameters, conditions of from 120 to 180° C. under a pressure of from 40 to 200 bar on a strong ion exchanger in the presence of excess molar water amounts are selected. The excess process water is recirculated. Such conditions cause an increase of the differential pressure in the reactor and thus pressure surges, which eventually necessitates shut-down of the continuous reaction. Further, in the hydration of propene, hot spots in the catalyst bed were observed, which lead to by-products. To overcome these problems, the mentioned DE-A-35 12 518 describes the addition of a strong cationic surfactant, for which, however, the possibility of deactivation of the ion exchanger employed as catalyst is described in principle.
DE-A-38 01 275 describes the catalytic hydration of tertiary C4 and C5 olefins at moderately increased temperatures in the liquid phase. The reaction takes place in two or more serial tube reactors which contain an acidic ion exchanger. According to the Examples, the content of dimers in the product mixture is significantly decreased if from 0.2 to 5% by weight, based on the tertiary olefin to be hydrated, of tertiary C4 or C5 alcohol is added to the feed mixture. In this way, for example, a product mixture is obtained which has a maximum content of tertiary amyl alcohol of 26%.
The use of acidic ion exchanger loaded with an amphoteric element is described in EP-A-0 325 144. TAA is obtained in a fixed-bed reactor by the hydration of isoamylene, but the purity in the reaction mixture is only at up to 27% by weight. The proportion of dimers in the product mixture is clearly reduced in this way.
EP-A-0 325 143 also describes the preparation of TAA by the hydration of isoamylene on an acidic ion exchanger at a reaction temperature near the boiling point of isoamylene under the respectively set reaction pressure. This is effected without the addition of materials not involved in the reaction, especially without the addition of solvents. According to the Examples, a TAA content of up to 51% or a TAA yield of up to 46% is achieved for a synthesis in a fixed-bed reactor under normal pressure.
Can. J. Chem. Eng. 1993, 71, 821-823, describes the preparation of TAA in a fixed-bed reactor without the use of a solvent as a phase mediator. However, a maximum conversion of 12% is achieved.
All previously described processes share the disadvantage that the conversion of the process for the hydration of olefins is limited by the position of the chemical equilibrium. In all reactor types employed, the reaction space accommodates packings of solid catalyst particles which have a spherical or pellet-like design, for example, and are flowed around by the reactants. In the reactors having such a design, on the one hand, large pressure drops occur, and on the other hand, a homogeneous temperature distribution over the reactor cross-section does not occur. Another disadvantage is that there is no uniform concentration distribution over the reactor cross-section so that the yield of the desired final products is not optimum.
In contrast, the principle of reactive rectification has established as a method for achieving high conversions in thermodynamically limited material conversions. It is based on rectification running parallel with the reaction, whereby the higher boiling products come down in the column and are thus removed from the equilibrium. In addition, the heat dissipation in exothermic reactions can thus be controlled by the evaporation of the more volatile components, and the desired reaction temperature can be adjusted through the overall pressure.
The preparation of tertiary alcohols, especially tertiary amyl alcohol and tertiary butyl alcohol, by the hydration of the corresponding tertiary olefins by reactive rectification in the presence of an acidic ion exchanger is described in EP-A-0 415 310. In this case, the acidic ion exchanger is provided in a multitude of bags of a tissue band which is connected with a mesh wire structure of stain less steel for support, wherein the tissue band and the mesh wire structure are helically wound. The tissue band with the bags preferably consists of glass fibers. A drawback in this process is the fact that very different and in part little satisfactory results are obtained depending on the olefin employed and on the reaction conditions. For the conversion of isoamylene, for example, contents of only about 18 or 27% by weight of tertiary amyl alcohol are achieved in the bottoms of the column. Exact conversions or yields are not stated.
Ind. Eng. Chem. Res. 1997, 36, 3845-3853, also describes the synthesis of TAA with the catalytic packing described in EP-A-0 415 310 through a reactive rectification. Although high conversions, based on the isoamylene employed, are evidently achieved, the great disadvantage of poor reproducibility is present here too. A variability of ±20% is stated.
The above described wound bodies employed for the hydration of olefins by reactive rectification in EP-A-0 415 310 and Ind. Eng. Chem. Res. 1997, 36, 3845-3853, have some disadvantages: Due to the poor mixing and homogenizing properties of the wound bodies, there is no radial temperature and concentration equilibration over the column cross-section, on the one hand. On the other hand, due to the non-ordered flow form of the educts, products and by-products, a relatively large pressure drop over the packing occurs.
It has been the object of the present invention to provide a process which especially enables the preparation of tertiary alcohols by the hydration of the corresponding tertiary olefins with a high and reproducible conversion, with high purity of the alcohol in the reaction mixture, and a long service life of the catalyst employed.